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Old 17th October 2012, 05:52 AM   #471
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Post #444: No DC. Corrected response view is short window. Measurement was made with exponential sweep 2-2205Hz, 10485760 samples long 44.1kHz sample rate. Drive voltage was 26V RMS. Sample rate conversion to 4410Hz sample rate (1048576 sample) was used for IR recovery and spectral display.

Correction filters are FIR, results are linear phase. Correction applied to continuous signal results in highly coherent passage through system. Recording of band pass filtered square waves look much like test signal.



Early reflection 2ms is seen in raw monopole IR. Extended tale of raw dipole response is primarily dipole path length and associated cavity behavior.

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Andrew
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Old 18th October 2012, 03:00 PM   #472
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I'm having a bit of trouble with the plots of #444 also. The 3 EQs are essentially the same even though the unEQed responses are considerably different. Not much correction going on. (Or is this the response with correction??) I can see that the EQ time domain (is this EQ alone or woofer plus EQ?) is essentially a linear phase filter with the sin x/x ringing. Still, a linear phase correction convolved with the minimum phase woofer should look more like the previous time response just with more added pre-ringing.

Some more explanation would help.

David S.

Last edited by speaker dave; 18th October 2012 at 03:02 PM.
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Old 18th October 2012, 04:07 PM   #473
OllBoll is offline OllBoll  Sweden
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One thing I've wondered about 3 distributed dipoles vs 3 distributed monopoles:

If I understand correctly each dipole can be modeled as two monopoles with a distance D, and that if you distribute them and use EQ the in-room response can be made equal or close enough to equal.

What I wonder however is if this also is true for bass leaking outside the room? I listen fairly quiet and so reduced SPL won't be that much of a problem if I use them as dipoles, the main focus is to reduce noise for the neighbours.
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Old 18th October 2012, 04:26 PM   #474
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I would think that sound leakage would be a function of sound power of the sources. That is certainly the way that room acoustics people model it. We also know that the directivity difference between a dipole and a monopole is 4.8 dB (meaning a dipole has 4.8 dB less power response for the same axial SPL. Viewed another way the monopole is 4.8 dB louder on axis for the same radiated power).

This gets us back to the universal question of whether we set the systems up with the same axial SPL or the same power response? I tend to think we would (at LF) set for about the same power response and then there would be no difference for the neighbors.

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Old 18th October 2012, 04:33 PM   #475
OllBoll is offline OllBoll  Sweden
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In my case I will distribute to get roughly equal response everywhere in the room, what I wonder mainly is the room pressurisation node: will the dipoles not exciting that one mean that less sound leaks to adjacent rooms or will it be equal?
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Old 18th October 2012, 04:38 PM   #476
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Perhaps Earl will comment but as I recall, the SPL in an enclosed space is a direct function of the radiated power. The may only apply above the Schroeder frequency.
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Old 18th October 2012, 04:50 PM   #477
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Room acoustic properties (either mean alpha or room constant) and radiated sound power would define the SPL in the room (the transmitting room.) TL or wall transmission loss would determine the energy loss to the adjacent room. Finally the room acoustics of the adjacent (receiving) room would determine the SPL in that room.

If flanking paths exist it gets more complex but that is generally how the calculations go. I'm not aware that Schroeder frequency is ever considered but most acoustical tests are ideally done in large rooms with added diffusion.

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Old 18th October 2012, 04:53 PM   #478
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For each individual neighbor bass leakage is the function of excitation of one particular wall. In case of a dipole it may be higher.
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Old 18th October 2012, 05:04 PM   #479
gedlee is online now gedlee  United States
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Quote:
Originally Posted by john k... View Post
Perhaps Earl will comment but as I recall, the SPL in an enclosed space is a direct function of the radiated power. The may only apply above the Schroeder frequency.
John - correct, the leakage would be independent of the type of source used to create the SPL. This assumes that the SPL's in the room are adjusted to be the same. A monopole can excite a very low resonance that a dipole cannot and it is these very low tones that tend to be the leakiest. Hence, in practice, the higher efficiency of the monpole would tend to have more leakage SPL.

Regarding post #444, I too was bothered, initially, but I have concluded that the results shown could be possible, so I have nothing on which to conclude that they are not correct. If an adaptive DSP was setup to create a bandlimited linear phase result, then it could do that, exactly as shown, for any source.

In that case, it is an extremely interesting result, completly proving the point that EQ can overcome any differences in source types. LFs in a room are not about the type of source.
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Old 18th October 2012, 05:18 PM   #480
keyser is online now keyser  Netherlands
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Interesting discussion!

I've always wondered about the transmission of sound at low frequencies. At higher frequencies (above the Schroeder-frequency) I assumed it would be mainly a function of radiated power, but at lower frequencies I would assume standing waves play a role: at frequencies where there are standing waves, the pressures at the room-boundaries are the highest and thus walls would flex more and there would be greater sound-transmission. Of course this is all ignoring the mechanical/acoustical properties of the room boundaries. Could anybody fill me in?
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